Electrical well logging



Patented Oct. 12, 954

ELECTRICAL WELL LOGGING Gherardo Bartolini Salimbeni, Florence, Italy No Drawing. Application September 20, 1952, Serial No. 310,720

Claims.

This invention relates to electrical well logging and its object is to provide a method for the detecting of minerals in the subsoil by effecting electric or inductive loggings after the addition to the drilling mud into the bore hole of suitable soil-modifying reagents, viz. reagents capable of reacting with at least some of the materials of the walls of the bore hole and modifying the electrical characteristics of the bore wall in that region. The curves obtained by the electrical logging effected after the reaction of the said soil-modifying reagents are compared with the curves obtained, under the same conditions, before the action of said reagents.

This method is particularly adapted for detecting those minerals or ores whose physical and chemical characteristics are such as not to permit of electrically differentiating them from the surrounding materials so that it is not possible to detect same with sufficient reliability by the usual electrical logging methods. This is for example, the case of sulphur embedded in calcium sulphate.

According to the invention the reagents employed for modifying the electrical characteristics of the subsoil surrounding the bore hole are usually strong oxydizing reagents, particularly those which do not substantially change the conductivity of the mud as, for example, by increasing the salinity thereof. In some cases reduction reagents or even other reagents, such as acids or bases might be employed, provided they be adapted to modify the electrical characteristics of the subsoil parts surrounding the bore hole without materially changing the conductivity of the mud.

Among the soil-modifying reagents, which have been found to be adapted for use in the practice of the method according to the invention, better results have been obtained by using organic oxidants of the class of the chloramines, viz. organic generally aromatic compounds containing the group --NC12 or -Nl-IC1 and particularly a substance having the formula CO2H.C6H4.SO2.NC12 or carboXy-benzene-sulphon-dichloramide, viz. a derivative of the dichloramine T (toluene sulphon dichloramide CI-Is.C6H4.SOz.1\TCh) in which the CH3 has been oxidized to COO'I-I.

Among the substances whose electrical characteristics have been found to be substantially modified by treatment as described so as to be readily detectable upon comparison of logs taken before treatment and after treatment, I may cite all oxidizable ores, such as sulphur and sulphides, manganese ores, including manganese dioxide, iron ores, including pyrites and hematite, mercury ores, and mineral substances of organic origin such as coals, oils, bituminous shales, &c. and generally all substances adapted to be more or less readily attacked by said soilmodifying reagents.

In the practice of this invention one proceeds as follows:

After having drilled the bore hole which contains the drilling mud, the usual electrical log is lowered and the usual curves of resistivity, self-potential and/or other electrical characteristics are recorded as usual.

Then a suspension of a chloramine in water is mixed to the drilling mud in the bore hole, usually in a proportion of about 2 grams per liter of mud and allowed to react from 5 to 30 minutes, according to the materials to be treated and/or to be detected. Then the electrical logging is repeated one or more times under the same conditions as those above described. In this manner two or more sets of curves are obtained, one set before treatment with the cloramine or other soil-modifying reagent and the other set or sets of curves after said treatment. The plurality of curves taken after the treatment will show the electrical characteristics of the well at intervals after initiating treatment by the reagent.

By comparing the dififerent sets of curves, it may be seen at what depth of the bore hole the soil-modifying substances have reacted more readily or more profoundly, thus giving by a differential logging an exact indication of the subsoil zones whose coring or more particular exploration is worth while.

Of course, in some cases, especially after a number of differential loggings in a zone, it will be possible to eliminate the first logging, viz. that before the treatment with the soil-modifying reagent.

It remains understood that, according to the invention, the term soil-modifying substance shall include not only the oxidizing compounds of the class of the chloramines, but any substance (as bromine) or compound which, without substantially increasing the conductivity or substantially modifying other electrical characteristics of the drilling mud contained in the bore hole, is capable of reacting with the materials of the walls of the bore hole, up to certain depth, so as to sensibly modify their electrical characteristics.

Among the substances that, under favorable circumstances, work in the described manner, there may be mentioned also acid and basic reagents, especially slightly soluble ones, as well as oxydizing or reducing substances which, by reacting with some of the soil components, modify their electrical characteristics.

I claim:

1. A method of locating subsurface formations of certain characteristics along a well bore which comprises; electrically logging the well, adding to the drilling mud in the well a reagent which is characterized in that it will react with the soil of the said formation and change the electrical characteristics thereof but will not subsubstantially alter the electrical characteristics of the drilling mud, and again electrically logging the well whereby the results of the loggings can be compared to locate the said formation.

2. The method of locatin subsurface formations of certain characteristics along a well bore, the general characteristics of which are known by Way of electrical logging thereof, which comprises; adding to the drilling mud in the well a reagent which will react with the soil of the said formation and substantially change the electrical characteristics thereof, but which will not substantially change the electrical characteristics of the drilling mud, and electrically logging the well a predetermined time after the addition of the reagent to the mud, whereby the characteristics obtained by the said logging can be compared with the known characteristics as obtained by logging the well prior to treatment thereof to locate the said formation.

3. A method according to claim 1 in which the said reagent is a nonionized organic oxidant which is only slightly soluble in water.

4. A method according to claim 2 in which the said reagent is a nonionized organic oxidant which is only slightly soluble in Water.

5. A method according to claim 1 in which the said reagent is an oxidant selected from the class of organic compounds containing an amine group in which at least one hydrogen of the amine is substituted by a halogen.

6. A method according to claim 2 in which the said reagent is an oxidant selected from the class of organic compounds containing an amine group in which at least one hydrogen of the amine is substituted by a halogen.

7. A method according to claim 1 in which the said reagent is a dichloramine which is employed in the proportion of about one to three grams for each liter of drilling mud in the well bore.

8. A method according to claim 2 in which the said reagent is a dichloramine which is employed in the proportion of about one to three grams for each liter of drilling mud in the well bore.

9. A method according to claim 1 in which the said reagent is the p. carboxy-benzene-sulphondichloramide.

10. A method according to claim 2 in which the said reagent is the p. carboxy-benzene-sulphon-dichloramide.

References Cited in the file of this patent Hartline May 6, 1952 

